Generally, an automatic transmission for vehicles controls shifting to automatically attain an optimal shift speed based on the driving conditions.
As is known in the art, a shift control is basically performed according to a shift pattern including a plurality of shift lines defined as a function of throttle opening and vehicle speed. More particularly, conventional shift pattern for a shift control is composed of two kinds of shift lines, upshift lines and downshift lines.
Because the upshift line of the conventional shift pattern is optimally determined mainly with respect to the vehicle speed change, it cannot provide an optimal shift pattern for an upshift due to a throttle opening change such as a lift-foot-up (LFU) upshift. For example, if a throttle change occurs in a third speed by a lift-foot-up (LFU), 3 to 4 to 5 to 6 upshifts are sequentially performed. Then, until a vehicle stops after the LFU, 6 to 5 to 4 to 3 to 2 to 1 downshifts are sequentially performed. That is, after the LFU, unnecessary downshifts are sequentially performed in a low vehicle speed. In particular, because a shift pattern for an automatic transmission having many shift speeds, such as a 6-speed or 7-speed automatic transmission, has many more shift lines, a small throttle opening change may cause frequent shifting.
In addition, the downshift line of the conventional shift pattern is optimally determined mainly with respect to a throttle opening change, it cannot provide an optimal shift pattern for a downshift due to a decrease of vehicle speed. That is, when a vehicle speed is decreased regardless of a driver's intention, e.g., when a vehicle drives upslope, a downshift does not occur even while vehicle speed decreases substantially. For example, when vehicle speed change occurs in a sixth speed under a state of about 40% of throttle opening, a downshift does not occur while vehicle speed decreases substantially.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.